PLANKTONIC STUDIES. 593 
_ Radiolaria.—No class of organisms has remained so long unknown 
to us, and by the brilliant discoveries of the last decade has been sud- 
denly placed in so clear a light, as the Radiolaria (comp. 4, § 251-260). 
For half a century we knew next to nothing of these wonderful rhizo- 
pods; to-day they appear as one of the most important planktonic 
classes.* These, the most varied in form of all the unicellular organ- 
isms, form a purely oceanic class, and live and swim in all seas, especially 
in the warmer ones. Numerous species are also found near the coasts, 
yet these are not distinguishable from those of the open sea. They 
constitute no separate neritic fauna. 
Vast crowds of Radiolaria oceur at the surface of the ocean, as well 
as at different depths. Long ago Johannes Miiller remarked: 
It is a great phenomenon that Acanthometra can be taken daily by thousands in a 
calm sea and independently of storms; and that of many species of Polycystina, 
hundreds of individuals were seen during my last residence at the seashore (2, p. 25). 
I have tried myself, on the hundreds of voyages to different coasts 
which 1 have made since 1856, to thoroughly study the natural history 
of the Radiolaria. The incomparable collections of the Challenger 
afforded me by far the richest material for observation. The results 
obtained therefrom are embodied in the report (1887). Among other 
references to the conditions of the plankton there mentioned, it brought 
up the following propositions: (1) Radiolaria occur abundantly in all 
seas which contain a medium amount of salt, and which do not (like 
the Baltic) receive a strong influx of fresh water. (2) In the colder 
seas only a few species occur (chiefly Acantharia), but immense quan- 
tities of individuals; towards the equator the variety in form gradu- 
ally increases (horizontal distribution, comp. 4, § 226-231). (3) The 
chief groups of Radiolaria are distributed unequally in the five bathy- 
zones or girdles of depth of the open ocean. The subclass Porulosa 
(the two legions of Spumellaria and Acantharia) inhabit especially the 
two upper zones. On the other hand, the subclass Osculosa (Nassetaria 
“After Ehrenberg, in 1847, had described the siliceous shells of some hundred 
species from the Barbados, we obtained in 1858 the first description of their organ- 
ization through Johannes Miiller. In the work with which this great master closed 
his renowned life he described 50 species which he had observed alive in the Med- 
iterranean Sea (2). When in continuation of this I devoted a winter’s residence 
in Messina to their further investigation, I was able in 1862, in the monograph con- 
sequent thereupon, to distinguish 144 new species, in all 113 genera and 15 families (8). 
But this rich Radiolaria fauna of Messina still gave no promise of the immense quan- 
tities of these delicately ornamented creatures peopling the open ocean, and 
whose variously formed siliceous shells, sinking to the bottom after death, formed 
that wonderful sediment, the ‘‘Radiolaria ooze.” This was first discovered thirteen 
years later by the Challenger. The investigation of the fabulous radiolarian treas- 
ures (chiefly from the Pacific) which this expedition brought home has led to the 
discrimination of 20 orders, 85 families, 739 genera, and 4,318 species (4, § 256). 
Further study of the Radiolaria slime of the deep sea will bring to light many new 
forms from this inexhaustibly rich mine, 
H, Mis. 1183——38 
